U.S. Pat. No. 4,207,424 describes a process for the catalytic dehydration of alcohols to form unsaturated organic compounds in which an alcohol is dehydrated in the presence of alumina catalysts which are pre-treated with an organic silylating agent at elevated temperature. Example 12 relates to ethanol, the WHSV is 1.2 h−1 and shows only a conversion increase by comparison with the same alumina but having not been pretreated.
U.S. Pat. No. 4,302,357 relates to an activated alumina catalyst employed in a process for the production of ethylene from ethanol through a dehydration reaction. In the description LHSV of ethanol is from 0.25 to 5 h−1 and preferably from 0.5 to 3 h−1. The examples are carried out at 370° C. and LHSV of 1 h−1, ethylene yield is from 65 to 94%.
Process Economics Reviews PEP' 79-3 (SRI international) of December 1979 describes the dehydration of an ethanol-water (95/5 weight %) mixture on a silica-alumina catalyst in a tubular fixed bed at 315-360° C., 1.7 bar absolute and a WHSV (on ethanol) of 0.3 h−1. The ethanol conversion is 99% and the ethylene selectivity is 94.95%. It also describes the dehydration of an ethanol-water (95/5 weight %) mixture on a silica-alumina catalyst in a fluidized bed at 399° C., 1.7 bar absolute and a WHSV (on ethanol) of 0.7 h−1. The ethanol conversion is 99.6% and the ethylene selectivity is 99.3%.
U.S. Pat. No. 4,232,179 relates to the preparation of ethylene, based on a process for dehydrating ethyl alcohol. More particularly, the object of said prior art is the production of ethylene in the presence of catalysts, using adiabatic reactors and a high temperature. Such adiabatic reactors may be used in parallel or may be arranged in series or arranged in assemblies of parallel series, or still only a single reactor may be used. The ratio between the sensible heat carrying stream and the feed may range from 0.2:1 to 20:1, but preferably shall be comprised within the range from 0.2:1 to 10:1. On the other hand the space velocity may range between 10 and 0.01 g/h of ethyl alcohol per gram of catalyst, depending on the desired operation severity, the range between 1.0 and 0.01 g/h/g being particularly preferred. In the examples the catalysts are silica alumina, the WHSV on ethanol is from 0.07 to 0.7, the ratio of steam to ethanol is from 3 to 5.
EP 22640 relates to improved zeolite catalysts, to methods of producing such catalysts, and to their use in the conversion of ethanol and ethylene to liquid and aromatic hydrocarbons, including the conversion of ethanol to ethylene. More particularly this prior art relates to the use of zeolite catalysts of Si/Al ratio from 11 to 24 (in the examples) such as the ZSM and related types in the conversion reaction of aqueous and anhydrous ethanol to ethylene, of aqueous ethanol to higher hydrocarbons, and of ethylene into liquid and aromatic hydrocarbons. WHSV ranges from 5.3 to 6 h−1, in dehydration to ethylene the reactor temperature is from 240 to 290° C.
U.S. Pat. No. 4,727,214 relates to a process for converting anhydrous or aqueous ethanol into ethylene wherein at least one catalyst of the crystalline zeolite type is used, said catalyst having, on the one hand, channels or pores formed by cycles or rings of oxygen atoms having 8 and/or 10 elements or members. In the examples the atomic ratio Si/Al is from 2 to 45, the temperature from 217 to 400° C. and the WHSV 2.5 h−1.
U.S. Pat. No. 4,847,223 describes a catalyst comprising from 0.5 to 7% by weight of trifluoromethanesulfonic acid incorporated onto an acid-form pentasil zeolite having a Si/Al atomic ratio ranging from 5 to 54 and a process for producing same. Also within the scope of said prior art is a process for the conversion of dilute aqueous ethanol to ethylene comprising: flowing said ethanol through a catalyst comprising from 0.5 to 7% by weight of trifluoromethanesulfonic acid incorporated onto an acid-form pentasil zeolite having a Si/Al atomic ratio range from 5 to 54 at a temperature ranging from 170° to 225° C. and recovering the desired product. The WHSV is from 1 to 4.5 h−1. The zeolites which are directly concerned by said prior art belong to the family called ZSM or pentasil zeolite family namely ZSM-5 and ZSM-11 type zeolites.
U.S. Pat. No. 4,873,392 describes a process for converting diluted ethanol to ethylene which comprises heating an ethanol-containing fermentation broth thereby to vaporize a mixture of ethanol and water and contacting said vaporized mixture with a ZSM-5 zeolite catalyst selected from the group consisting of:                a ZSM-5 zeolite having a Si/Al atomic ratio of from 5 to 75 which has been treated with steam at a temperature ranging from 400 to 800° C. for a period of from 1 to 48 hours;        a ZSM-5 zeolite having a Si/Al atomic ratio of from 5 to 50 and wherein La or Ce ions have been incorporated in a weight percentage of 0.1 to 1.0% by ion exchange or in a weight percentage ranging from 0.1 to 5% by impregnation, and        a ZSM-5 zeolite having a Si/Al of from 5 to 50 and impregnated with a 0.5 to 7 wt % of trifluoromethanesulfonic acid,and recovering the ethylene thus produced.        
In ex 1 the catalyst is a steamed ZSM-5 having a Si/Al ratio of 21, the aqueous feed contains 10 w % of ethanol and 2 w % of glucose, the temperature is 275° C., the WHSV is from 3.2 to 38.5 h−1. The ethylene yield decreases with the increase of WHSV. The ethylene yield is 99.4% when WHSV is 3.2 h−1 and 20.1% when WHSV is 38.5 h−1.
In ex 2 a ZSM-5 having a Si/Al ratio of 10 is compared with the same but on which La or Ce ions have been incorporated. The aqueous feed contains 10 w % of ethanol and 2 w % of glucose, the temperature is from 200° C. to 225° C., the WHSV is 1 h−1 and the best ethylene yield is 94.9%.
In ex 3 the catalyst is a ZSM-5 having a Si/Al ratio of 10 on which trifluoromethanesulfonic acid has been incorporated, the aqueous feed contains 10 w % of ethanol and 2 w % of glucose, the temperature is from 180° C. to 205° C., the WHSV is 1 h−1. The ethylene yield increases with temperature (73.3% at 180° C., 97.2% at 200° C.) and then decreases (95.8% at 205° C.).
U.S. Pat. No. 4,670,620 describes ethanol dehydration to ethylene on ZSM-5 catalysts. In a preferred embodiment the catalysts used according to this prior art are of the ZSM-5 type and preferably at least partially under hydrogen form. In the examples the catalyst is a ZSM-5 or a ZSM-11 having a SI/Al ratio of 40 to 5000 (ex 13), the LHSV is from 0.1 to 1.8 h−1 and the temperature from 230° C. to 415° C.
JP 2007-290991 A1 describes the conversion at 500° C. of an ethanol dimethylether mixture on a P—ZrO2/ZSM-5 and W—ZrO2/ZSM-5 to make a mixture of ethylene, propylene and butene.
EP 1396481 describes a process for converting a hydrocarbon feedstock to provide an effluent containing light olefins, the process comprising passing a hydrocarbon feedstock containing at least one C1 to C4 aliphatic hetero compound selected from alcohols, ethers, carbonyl compounds and mixtures thereof through a reactor containing a crystalline silicate catalyst to produce an effluent including propylene, the crystalline silicate being selected from at least one of an MFI-type crystalline silicate having a silicon/aluminium atomic ratio of at least 180 and an MEL-type crystalline silicate having a silicon/aluminium atomic ratio of from 150 to 800 which has been subjected to a steaming step. In the examples only methanol is used, the reaction temperature is between 400 and 550° C. and the effluent is a mixture of ethylene, propylene, C4 olefins, C5 olefins and aromatics.
U.S. Pat. No. 3,911,041 relates to a process wherein methanol and dimethyl ether are converted to a reaction product containing olefins. The conversion is carried out employing a catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12, a constraint index of about 1 to 12, and containing phosphorus incorporated with the crystal structure thereof in an amount of at least about 0.78 percent by weight. Only methanol and dimethylether are used in the examples. This conversion is similar to the one described in the above EP 1396481 except the catalyst.
It has now been discovered that the dehydration of at least an alcohol to at least an olefin can be made:    on a crystalline silicate having a high Si/Al ratio at least 100 or    on a dealuminated crystalline silicate or    on a phosphorus modified zeolite and    with a WHSV of at least 2 h−1.
By way of example, in the dehydration of ethanol on a crystalline silicate having a high Si/Al ratio at least 100 and with a WHSV of at least 4 h−1 to make ethylene, the ethanol conversion is at least 98% and often 99%, advantageously the ethylene yield is at least 97%, the ethylene selectivity is at least 96% and often 97% and the ethylene purity is at least 99% and often 99.8%.    The ethanol conversion is the ratio (ethanol introduced in the reactor−ethanol leaving the reactor)/(ethanol introduced in the reactor).    The ethylene yield is the ratio, on carbon basis, (ethylene leaving the reactor)/(ethanol introduced in the reactor).    The ethylene selectivity is the ratio, on carbon basis, (ethylene leaving the reactor)/(ethanol converted in the reactor).
The ethylene purity is the ratio, on carbon basis, (ethylene leaving the reactor)/(ethylene+ethane leaving the reactor). It means the ethylene purity is the percentage of ethylene, on a carbon basis, present in the C2 cut, containing close-boiling compounds, recovered in the stream leaving the reactor. The C2 cut doesn't comprise the unconverted ethanol and acetaldehyde if any. The same definitions apply mutatis mutandis to the alcohol and the olefin.